Wooden members have been stained or painted for many years to emphasize the natural grain of wood or to produce a pleasing, attractive, decorative color in the wood.
The invention relates to a chemical process that develops an attractive colored appearance that emphasizes the natural beauty of the wood. The invention does not relate to opaque coatings such as paints. Commonly available stain compositions typically comprise a solution or dispersion of a colorant or dye in a vehicle designed primarily to be applied to a surface of a wood article to impart color rather than to form a protective coating. Stains are typically different than paints and other coatings since stains are decorative and do not form opaque coatings. The colorant or dye in the stain composition, when contacted with a wooden surface, typically associates either physically or chemically with the wood surface. The coloring effect results from absorption, mechanical admixture, entrapment, or dipolar attraction of the colorant and the cellulosic wood constituents. Often reactions between the dye and the binder can occur in combination with the cellulose or the dye and binder can be physically associated with the cellulose.
Commonly available stains are typically characterized as non-grain-raising stains, oil stains (both penetrating and non-penetrating), spirit stains and water stains. These classifications generally refer to the vehicle which forms the dispersing media for the dye or colorant. Both organic and inorganic dyes and colorants are used and include such compositions as FD&C RED #1, FD&C Blue #1, rhodamine B, methylene blue, phthalocyanine, ultramarine, iron oxides, and others.
In the application of conventional stains to wood members typically an amount of the stain composition is applied to a brush, rag or other application implement, the stain is applied to the surface of the wood member, the implement is used to insure a complete contact between the stain composition and the wood member, and the excess stain is removed using a wash or other cleaning means such as a rag or cloth. Such processes can be inconvenient since they can result in stain contacting persons applying the stain to the wood member, can be dangerous since the stain can contain toxic or other harmful dye or vehicle compositions, and can waste the stain composition since excess stain, which must be removed from the wood member, is typically discarded. Soft woods such as pine, fir, and other evergreens can be difficult to stain and obtain a pleasing and uniform appearance.
The treatment of oak with gaseous ammonia is known, however this process is limited to oak and produces a particular fumed oak appearance. Brazilian Pat. App. No. PI 8402434 teaches darkening clear hardwood for increasing the quality, refinement and appearance of the wooden product by immersing logs, sheets, boards having a thickness of at least 0.2 millimeters in a tank of water which is heated gradually from about 60.degree. C. to 160.degree. C. during a time period of 48 to 168 hours. Such a process is time consuming and requires equipment that will gradually raise the temperature. More importantly, we have discovered that the use of water alone does darken wood, however the final product can be seriously degraded even after a brief treatment. We find that the degradation results from the formation of low pH's, about 3-4. The color resulting from the water treatment can often be dark and unpleasing in appearance.
Accordingly, a substantial need exists in the art for a rapid chemical process that can form a decorative attractive natural-appearing color without the need of the use of colorants, dyes or vehicles. A desirable process for producing a natural-appearing color is free of dyes, involve only moderate reaction conditions and protect operating personnel and equipment from contact with undesirable dyes and solvent compositions.